John Arnold

Net Worth: $3 billion
Coming off of a tough year in 2010, this hedge fund manager introduced a new, leaner management fee of just 1.5% in 2011 and produced net returns of 9% in what would prove to be his final year in the hedge fund business. Rather than trading natural gas, Arnold has spent 2012 winding down his fund, Centaurus Advisors. In a letter to shareholders announcing his decision, the “king of natural gas” expressed a desire “to pursue other interests.” Philanthropy seems to be at the top of the list for now. His Laura and John Arnold Foundation has more than $700 million in assets according to the organization's most recent tax filing, stemming from nearly $600 million in contributions from the Arnolds. Arnold got his start trading oil at Enron in 1995 and is said to have earned $750 million for the company in 2001. When the energy outfit famously collapsed a year later, he went into business for himself, founding Centaurus. He bought up hedge fund Amaranth Advisors' losing positions in natural gas in 2006 in the trade that propelled him to billionaire status.